High speed motorized spindles were initially developed for precision grinding and over the years have been used for other machining operations involving heavy stock removal such as rotary milling, end milling and end facing. Such high speed spindles have been used in conjunction with machining centers having multiple tool storage and tool changer mechanisms for exchanging one type of tool for another on the prime spindle of the machining center. U.S. Pat. No. 3,803,981 issued Apr. 16, 1974 to Allgeyer illustrates a sub-spindle mounted in a prime spindle. Similarly, U.S. Pat. No. 4,077,736 describes an electric motor driven drill in the toolholder of a machine tool.
There is a need to provide a high speed spindle with a self-contained or built-in tool clamping/unclamping mechanism so that an individual tool chucked in the high speed spindle can be readily exchanged with another tool, especially one for use as an auxiliary high speed spindle loaded into the prime spindle of a machining center application.
Typical prior art high speed spindle constructions are illustrated in the Moore U.S. Pat. No. 2,502,874 issued Apr. 4, 1950, the Arms U.S. Pat. No. 2,523,983 issued Sept. 26, 1950, the Bryant et al. U.S. Pat. No. 2,550,908 issued May 1, 1951 and the Grobey U.S. Pat. No. 2,819,127 issued Jan. 7, 1958, the Mitchell et al. U.S. Pat. No. 3,929,944 issued Feb. 24, 1976 and the Mitchell U.S. Pat. No. 4,211,454 issued July 8, 1980.